1. Field of the Invention
This invention pertains to a method and apparatus for mechanically treating sutures, and especially to a method and apparatus for calendering multifilament surgical sutures.
2. Background of the Art
An important consideration in performing surgery is the "hand" or "feel" of the suture being used to close wounds, which is reflected at least in part by the knot tie-down and run-down characteristics of the suture. "Tie-down characteristics" refers to the facility with which a surgeon can tie a knot, and the ability of the suture to remain knotted without spontaneously unravelling. "Run-down characteristics" refers to the ability of a surgeon to make one or more "throws" of a knot in the suture and have it run down a suture to the knot site. Generally, hand or feel of a suture and tie-down characteristics relate to the lubricity and stiffness of the suture: lubricity facilitates the tying of a knot whereas stiffness makes tying a tight knot more difficult and increases the probability of kinking of the suture and/or unravelling of the knot.
Both multifilament sutures and monofilament sutures are known in the art. Multifilament sutures, such as braided or twisted sutures, have better softness and flexibility than monofilament sutures and can be more easily knotted. However, multifilament sutures can have a rougher surface or "grabbiness" than monofilament sutures and a significant percentage of dead space or interstices between the filaments. The dead space can be reduced by impregnating the multifilament suture with a filler material. Filler material can help lubricate the suture fibers and enhance flexibility.
Coatings improve the knot run down characteristics of a suture, although they also tend to increase stiffness. Another source of stiffness arises from the commonly employed process of "heat setting" or "hot stretching" the suture, such as described in U.S. Pat. Nos. 3,322,125, 3,257,702, 3,379,552, and 3,839,524, for example. It has been proposed to improve the flexibility of heat set sutures by flexing the suture as disclosed in U.S. Pat. Nos. 3,839,524, and 3,257,702.
Known materials for filling or coating sutures are described in U.S. Pat. Nos. 3,322,125, 3,379,552, 3,867,190, 3,942,532, 4,047,533, 4,532,929, 4,201,216, and 4,711,241, for example.
However, the uniformity of the filling or coating remains as an important concern in the fabrication of sutures. Non-uniformity can hamper the effectiveness of the filler and coating, and an apparatus and method which addresses this issue is needed.